1. Field of the Invention
The present invention relates to a system for the downhole separation of fluids and, more particularly, to such a system that separates oil from water within a wellbore and that disposes of the separated water within the wellbore.
2. Description of Related Art
In many oil fields around the world the percentage of water recovered with oil from subterranean wellbores has risen to be greater than the percentage of the oil. In fact, in many fields, the percentage of oil has decreased to be from about 20% in an excellent field to about 2% in a relatively poor field. Therefore, the operator must lift to the surface and then dispose of the resulting tremendous volume of water. This situation wastes energy because of the power needed to operate pumps to lift and separate the water, and causes an environmental problem. In many locations the separated water cannot be disposed of on the surface, so the water must be transported to a remote well site to be reinjected into a subterranean formation. There is a need for a method and related system for separating the oil from water downhole so that the quantity of water recovered to the earth's surface can be minimized, and hopefully, eliminated.
One method of downhole oil and water separation is disclosed in U.S. Pat. Nos. 5,296,153 and 5,456,837, wherein wellbore fluids are drawn through a hydrocyclone that separates the oil from water. An actual field installation configuration of such a prior system is shown in FIG. 1 hereof. The separated water is then introduced into a first pump to force the water into a subterranean formation, that is isolated from the formation from which the oil and water mixture is recovered from. The separated oil is introduced into a second pump to force the oil to the earth's surface for processing.
A significant disadvantage of the method disclosed in U.S. Pat. No. 5,296,153 is that the oil and water mixture must be drawn through the hydrocyclone and then introduced into a pump. Further, the separated water must exit the separator and be conveyed to a remote location within the wellbore. This arrangement results in a significant loss of fluid head, so the loss in pumping efficiency limits the ability of the system to be used in higher volume wells and results in a waste of energy. There is a need for a method and related system that efficiently separates oil from water within a wellbore, and that efficiently disposes the separated water into subterranean formations.
Additionally, the system disclosed in the '153 Patent presents problems with diametric clearances in wellbores. For example, in a 7 inch diameter casing, it is current practice to install an electric submergible pumping system of 5.62 inches in diameter. The resulting diametric clearance is insufficient to have fluid transfer tubes outside of the exterior profile of the pumping equipment, as is needed when fluids are to be recovered from a lower zone and injected into an upper zone, without using smaller than desired pumping equipment. If the smaller sized equipment is used, the fluid transfer tubes located outside of the pumping equipment are prone to damage when installing or removing the pumping equipment. Further, a problem with the prior hydrocyclone configurations is that a series of complicated and relatively expensive cast manifolds and formed tubing must be used, which significantly add to the cost of the system.